Method and system for preventing intradialytic symptomatology

ABSTRACT

Methods and apparatus are disclosed for conducting blood treatment procedures. The method includes conducting the treatment procedure such as dialysis at a first efficiency until a limit value is reached, and then altering the first efficiency to a second efficiency until a second limit value has been reached. The method also includes devising a predetermined efficiency profile for the blood treatment procedure, conducting the procedure at a predetermined efficiency until a first limit value is reached, and then altering the efficiency of the blood treatment procedure in accordance with the predetermined efficiency profile.

FIELD OF THE INVENTION

The present invention relates to the field of preventing intradialyticsymptomatology during dialysis, such as hemodialysis, hemodiafiltrationor hemofiltration, including both continuous and acute therapy.

BACKGROUND OF THE INVENTION

One intradialytic symptom is the disequilibrium syndrome which was firstdescribed in 1961. The disequilibrium syndrome is a set of systemic andneurologic symptoms that can occur either during or soon after dialysis.Early symptoms are nausea, vomiting, restlessness and headache, followedby seizures, obtundation and coma. Some believe that the cause isrelated to an acute increase in brain water content, while othersbelieve that the cause relates to acute changes in the pH of thecerebrospinal fluid during dialysis. This problem is exacerbated whenacute patients with very high plasma urea nitrogen values are subject toa dialysis which is too efficient.

The treatment for mild symptoms is to decrease the efficiency of thesolute removal and pH changes, such as by reducing the blood flow.Hypertonic NaCl or glucose can also be administered.

With more severe symptoms, the dialysis session should be stopped.Intravenous mannitol may also be of benefit.

The disequilibrium syndrome can be avoided by using high NaClconcentrations of at least 140 mmol/l and by using glucoseconcentrations of at least 200 mg/dl. Decreasing the sodium dialysissolution during dialysis treatment has also been suggested.

Another common intradialytic complication is symptomatic hypotension,which is normally related to an excessively rapid decrease in the bloodvolume during dialysis. Today most dialysis machines use a volumecontrol for ultrafiltration, which is a method which aids in preventingsymptomatic hypotension. Other methods include the profiling of sodium,use of low temperature, switching from acetate to bicarbonate, etc.

Furthermore, ultrafiltration below the patient's dry weight may resultin symptomatic hypotension associated with, for instance, cramps,dizziness, malaise and a washed-out feeling.

An object of the present invention is to solve these and relatedintradialytic complications during dialysis.

Biofeedback is a subject which is being investigated by manyresearchers. One example is U.S. Pat. No. 4,469,593 which discloses ablood purification apparatus including a hematocrit measurementapparatus. The hematocrit value is used for controlling a negativeultrafiltration pressure on the dialysate side of a dialyzer formaintaining the hematocrit value constant or according to a pre-definedprofile. Also the conductivity of the blood or plasma is used in orderto establish an upper limit for sodium, while the hematocrit valuecontrols both the addition of replacement fluid and for increasing thesodium concentration in a hemofiltration apparatus. Finally, the oncoticpressure is also used for biofeedback.

International Patent No. WO 94/08641 discloses an on-line real time ureasensor which is used to measure the urea concentration in the effluentfrom a dialyzer. The system establishes two exponential fits of the ureaconcentration, with an early fit during the first 30 minutes and a latefit during the flowing treatment time. By obtaining an initialBUN-value, the Kt/V or SRI (solute removal index) can be calculated andprojected to the intended time. In this way, the efficiency of thetreatment can be measured on line. It is stated that the efficiencydecreases at all times during the treatment time, although presumablymore slowly at the end. It is also stated that deviation from aprojected Kt/V value can be used for troubleshooting.

International Patent No. WO 95/32010 discloses a method of determiningthe optimum blood flow (as measured by pump speed) in order to obtainthe most efficient dialysis. It is observed that the efficiency orclearance of the dialyzer is dependent on the blood flow rate (anddialysis flow rate, as well as temperature, etc.). However, above apredetermined blood flow, the efficiency of the dialyzer once againdecreases. There are several factors for this phenomenon, one of whichis fistula recirculation. According to International Patent No. WO95/32010, the efficiency of the dialyzer is determined at differentblood flows, for example in increments of 50 ml/min, and the blood flowat maximum clearance is used. The maximum blood flow is determined atthe start of each treatment. If this maximum blood flow declines after anumber of weeks or days, it can be a sign of fistula malfunction. Inthis specification, a urea sensor is used for assessing the efficiencyof the treatment at the start.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and apparatusfor performing dialysis or a similar treatment as fast as possible,while minimizing the inconvenience to the patient.

It has now been found that each patient has a characteristic curve formaximum tolerated treatment efficiency versus time. According to thepresent invention, the treatment is performed as efficiently as possibleuntil that curve is reached or approached, and thereafter the treatmentefficiency is decreased so that the curve is never reached.

In an alternative embodiment of the present invention, the dialysistreatment is preceded by isolated ultrafiltration. The dialysistreatment is performed with high efficiency until the characteristiccurve is approached. The continued treatment is then performed withdecreasing efficiency so that the curve is never reached.

In accordance with the present invention, these and other objects havenow been accomplished by the discovery of a method of conducting a bloodtreatment procedure comprising conducting the blood treatment procedureat a first predetermined efficiency until a first predetermined limitvalue has been reached, and altering the first predetermined efficiencyto a second predetermined efficiency until a second predetermined limitvalue has been reached. Preferably the second predetermined efficiencycomprises a predetermined efficiency profile including at least a thirdpredetermined efficiency.

In accordance with one embodiment of the method of the presentinvention, the method includes terminating the method upon reaching thesecond predetermined limit value.

In accordance with another embodiment of the method of the presentinvention, the first predetermined efficiency comprises a higherefficiency than the second predetermined efficiency.

In accordance with a preferred embodiment of the method of the presentinvention, the blood treatment procedure comprises dialysis. Preferablythe second predetermined limit value comprises a predetermined dialysisdosage.

In accordance with the present invention, a method has been discoveredfor conducting a blood treatment procedure comprising devising apredetermined profile of efficiency for the blood treatment procedure,conducting the blood treatment procedure at a predetermined efficiencyuntil a first predetermined limit value has been reached, and alteringthe efficiency of the blood treatment procedure in accordance with thepredetermined profile of efficiency. Preferably the blood treatmentprocedure comprises dialysis.

In accordance with one embodiment of the method of the presentinvention, the method includes devising a characteristic curve ofefficiency for a specific patient and determining the firstpredetermined limit value based upon reaching the characteristic curve.Preferably the method includes measuring the amount of urea removed bythe dialysis and determining the first predetermined limit value basedupon removal of a predetermined amount of the urea. In a preferredembodiment, the method includes determining a urea generation rate for aspecific patient and the predetermined amount of the urea is based uponthe urea generation rate.

In accordance with a preferred embodiment of the method of the presentinvention, the method includes determining the predetermined amount ofurea based upon the product of the urea generation rate, the timebetween the dialysis procedure and a second dialysis procedure, and apredetermined patient factor.

In accordance with another embodiment of the method of the presentinvention, the method includes measuring the concentration of urearemoved by the dialysis, and determining the first predetermined limitvalue based upon a predetermined concentration of the urea.

In accordance with another embodiment of the method of the presentinvention, the determining of the profile of efficiency for the bloodtreatment procedure comprises altering the flow of blood or the flow ofa dialysis fluid through a dialyzer. Preferably, the method includesdevising a characteristic curve of efficiency for a specific patient,wherein the determining of the profile of the efficiency for the bloodtreatment procedure is based upon a curve approaching the characteristiccurve. In a preferred embodiment, the determining of the profile of theefficiency is carried out stepwise or continuously.

In accordance with a preferred embodiment of the method of the presentinvention, the predetermined profile of the efficiency is based upon theurea concentration of the dialysis outlet fluid, and the determining ofthe profile of the efficiency for the dialysis is based upon maintainingthe urea concentration upon the predetermined profile.

In accordance with the present invention, apparatus has been discoveredfor conducting a blood treatment procedure comprising means forconducting the blood treatment procedure at a first predeterminedefficiency until a first predetermined limit value has been reached andmeans for altering the first predetermined efficiency to a secondpredetermined efficiency until a second predetermined limit value hasbeen reached. Preferably, the apparatus includes means for terminatingthe blood treatment procedure upon reaching the second predeterminedlimit value.

In accordance with the present invention, apparatus has been providedfor conducting a blood treatment procedure comprising means fordetermining a predetermined profile of efficiency for the bloodtreatment procedure, means for conducting the blood treatment procedureat a first predetermined efficiency until a first predetermined limitvalue has been reached, and means for altering the efficiency of theblood treatment procedure in accordance with the predetermined profileof efficiency. Preferably the blood treatment procedure comprisesdialysis.

In accordance with one embodiment of the apparatus of the presentinvention, the apparatus includes means for devising a characteristiccurve of efficiency for a specific patient and means for determining thefirst predetermined limit value upon reaching the characteristic curve.

In accordance with another embodiment of the apparatus of the presentinvention, the apparatus includes means for measuring the amount of urearemoved by the dialysis, and means for determining the firstpredetermined limit value based upon the predetermined amount of theurea removed. In a preferred embodiment, the apparatus includes meansfor determining a urea generation rate for a specific patient and meansfor determining the predetermined amount of urea removed based upon theurea generation rate. Preferably the apparatus includes means fordetermining the predetermined amount of the urea removed based upon theproduct of the urea generation rate, the time between the dialysis and asecond dialysis procedure, and a predetermined patient factor.

In accordance with another embodiment of the apparatus of the presentinvention, the apparatus includes means for measuring the concentrationof urea removed by the dialysis, and means for determining the firstpredetermined limit value based upon a predetermined concentration ofthe urea.

In accordance with another embodiment of the apparatus of the presentinvention, the means for determining the profile of efficiency for theblood treatment procedure comprises means for altering the flow of bloodor the flow of dialysis fluid through a dialyzer. Preferably theapparatus includes means for devising a characteristic curve ofefficiency for a specific patient, wherein the means for determining ofthe profile of the efficiency for the treatment procedure is based upona curve approaching the characteristic curve. In a preferred embodiment,the means for determining the profile of the efficiency is carried outstepwise or continuously.

In accordance with another embodiment of the apparatus of the presentinvention, the apparatus includes means for determining a predeterminedprofile, and wherein the means for determining the profile of theefficiency for the blood treatment procedure is based upon the ureaconcentration of the dialysis outlet fluid.

In accordance with another embodiment of the apparatus of the presentinvention, the blood treatment procedure is hemodialysis, hemofiltrationand hemodiafiltration.

BRIEF DESCRIPTION OF THE DRAWINGS

The PRESENT invention will be described in more detail with reference tothe following detailed description, which in turn refers to the drawingswherein:

FIG. 1 is a graphical representation of a typical characteristic curvefor a specific patient;

FIG. 2 is a graphical representation of an efficiency curve;

FIG. 3 is a graphical representation of a typical urea sensor outputcurve;

FIG. 4 is a schematic representation of a dialysis machine incorporatingthe present invention;

FIG. 5 is a schematic representation of a hemodiafiltration machineincorporating the present invention;

FIG. 6 is a schematic representation of a hemofiltration machineincorporating the present invention; and

FIG. 7 is a schematic representation of another hemofiltration machineincorporating the present invention.

DETAILED DESCRIPTION

According to the present invention, it has been found that a specificpatient being exposed to efficient dialysis, for example with the targetof Kt/V being equal to 2.0 or higher, will risk becoming symptomatic ifthe efficiency is too high and the dialysis time is too short. Forexample, a patient prescribed at Kt/V=2.0 during 4 hours will require anefficiency of K/V=0.5, which could result in the collapse of thispatient. However, if the time was increased to 5 hours and,consequently, the efficiency was decreased to K/V=0.4, then the patientcould stand the treatment without collapse or reaching his breakpoint.Other patients may become symptomatic even at lower Kt/V values and theefficiencies in the above figures are only given as an example.

It has now been found that a specific patient has a characteristic curveas shown in FIG. 1. If the curve is exceeded, the patient will breakdown. As can be seen from FIG. 1, it would not be possible to reach thegoal of Kt/V=2.0 in 4 hours without passing the characteristic curve.

It is probable that the characteristic curve is in fact a series ofcurves depending on other factors of the dialysis, such asultrafiltration rate, start BUN, sodium concentration or profiling,bicarbonate concentration, as well as psychological or physiologicalfactors, such as illness or depression, etc.

According to the present invention, the efficiency of the treatment isprofiled according to a specific profile adapted to the patient. Such aprofile could involve starting with as high efficiency as possible, forexample K/V=0.6 during one hour, then decreasing the efficiency stepwiseto K/V=0.5 during the second hour, K/V=0.4 during the third hour andK/V=0.3 during the last hour, which would result in a Kt/V value of 1.8during four hours. By on line measurement of the efficiency using a ureamonitor, the process can be monitored so that the desired efficiency isobtained in reality, and the efficiency can be adjusted automatically tofollow the desired profile.

In a preferred embodiment, the efficiency of the treatment is as high aspossible at the start, until a limit value is reached, which isindicative of the fact that the patient is approaching hischaracteristic curve and can no longer withstand high efficiencydialysis. After the limit value has been reached, the efficiency is thenchanged according to a predetermined curve. When the desired goal hasbeen obtained, the treatment is terminated.

The limit value can be determined in several ways. It can be determinedempirically so that the characteristic curve of a specific patient isdetermined by exposing him to different dialysis efficiencies andmonitoring specific patient data. In this manner, the limit value can beestablished by looking into the curve.

It is often not possible to expose a specific patient to such differentdialysis efficiencies, and to drive the patient to disequilibriumconditions merely in order to obtain a characteristic curve.

Another approach is to monitor the removal of urea by the urea monitor,and when a predetermined amount of urea has been removed, the limitvalue has been reached.

This amount of urea is obtained by integrating the values obtained bythe urea sensor, which are concentration values. If it can be assumedthat the dialysis fluid flow is constant, the total removed urea (TRU)is the integral of the concentration curve. Otherwise, the concentrationcurve can be multiplied by the volume flow of the dialysis fluid at anytime and then integrated to obtain the mass of urea removed.

The amount of urea can be a predetermined proportion of the ureaproduction between the dialysis sessions, for example, between about 50%and 90%, or preferably between about 65% and 80%, for example, about75%, of the urea generated between the dialysis treatments. Often it canbe assumed that the urea generation is fairly constant during a shorttime span, such as a week. Formulae are known for the urea generationfor hemodialysis patients, which can be used for initial determinationof this amount of urea removed for reaching the disequilibrium limitvalue.

Another approach to determining when the patient is close to hischaracteristic curve would be to monitor when the concentration in theblood reaches a predetermined lower value, which is indicative ofreaching that limit value. It is more convenient to monitor theconcentration in the dialysis fluid, which, however, is a mirror of theconcentration in the blood.

After reaching the limit value, the efficiency is changed. One approachis to decrease the efficiency step-wise, for example in increments offrom about 0.1 to about 0.01 for the efficiency K/V.

Another approach is to use an exponential declination of the efficiency,as is outlined in FIG. 2.

The urea monitor concentration values may be used for controlling theefficiency. From the start, the highest possible efficiency is allowed.When the concentration value at the urea monitor reaches a low value,indicative of approaching the characteristic curve, the efficiency iscontrolled or altered so that the urea monitor concentration valuefollows a predetermined curve, such as the efficiency curve of FIG. 2.

Consequently, the dialysis efficiency is adapted to the patient and tothe concentration gradient he can withstand across the brain barrierwithout breaking down. In this case, the concentration gradient isdependent on the initial concentration of urea in the brain, which,however, is dependent on the urea generation rate between the dialysissessions. If it is assumed that the urea generation rate is fairlyconstant, the predetermined low concentration value of the urea monitorcan be calculated in relation to the urea generation rate.

It is believed that the reason for reaching a time limit is the factthat the urea in the body is distributed between different compartments,for example extracellular and intracellular compartments. Urea in theextracellular compartment is readily available for dialysis by thehigh-efficiency dialysis process. When the urea in the extracellularcompartment has been rapidly removed, the urea concentration in theblood will be low. Consequently, there is a high concentration gradientover those membranes, which do not readily pass the urea molecule, suchas the brain barrier. Such high gradients are known to trigger thedisequilibrium syndrome. Moreover, such high gradients will cause waterto pass the brain barrier in the opposite direction, increasing theintracranial pressure, which may also induce the disequilibriumsyndrome.

If a higher efficiency is used from the start, the extracellularcompartment will be depleted faster without allowing the intracellularcompartment a sufficient time to give off any appreciable amount ofurea. On the other hand, if a lower efficiency is used from the start,the patient can withstand the dialysis for longer time, since theintracellular compartment has time to contribute to the urea in theblood. This suggests why increased efficiency cannot be tolerated for along period of time.

While this is a plausible explanation, we do not want to bind ourselvesto this explanation, since there are many other factors contributing tothe removal of urea. Moreover, urea is only one of the molecules removedduring a dialysis session, and it cannot be ruled out that othermolecules play an important role in the disequilibrium syndrome. Urea iscommonly used as a marker molecule for dialysis efficiency.

The dialysis efficiency can be influenced in several ways. The mostconvenient way is to change the blood flow rate, which has a direct,although non-linear relationship to the efficiency. It is also possibleto change the dialysis fluid flow rate, which gives approximately thesame results. Or both the blood flow rate and dialysis flow rate may bealtered. The same applies to hemofiltration and hemodiafiltration.

The dialysis efficiency is obtained by monitoring the urea concentrationin the outgoing dialysis fluid flow. A typical urea concentration curveis shown in FIG. 3. The slope of the logarithm of the curve correspondsin principle to the efficiency, K/V.

A typical dialysis machine is schematically shown in FIG. 4. Thedialysis machine 1 comprises a dialysis fluid preparation portion 2 anda blood flow portion 3.

The blood flow portion 3 comprises a pump 4 which propels the blood inthe extracorporeal blood circuit 5.

The dialysis fluid preparation portion 2 includes pumps, 6 and 7, whichcontrol the fluid flow rate of the dialysis fluid, as well as theultrafiltration pressure applied across a membrane 8 of a dialyzer 9.Two fluid flow meters, 10 and 11, determine the dialysis fluid flowrate, as well as the ultrafiltration flow obtained from the blood.

A urea monitor 12 is included in an outlet line 13 from the dialysismachine. The urea monitor is disclosed in details in InternationalPatent No. WO 96/04401, which is incorporated herein by referencethereto. The urea monitor 12 accurately determines the ureaconcentration in the outlet dialysis fluid line 13.

All signals from the flow meters, 10 and 11, pumps, 4, 6, and 7, andurea monitor 12 are fed to a computer 14.

The urea removal rate from blood is equal to the concentration times thedialysis fluid flow, since no urea is included in the incoming dialysisfluid. The total removed urea (TRU) is determined automatically by theurea monitor on a continuous basis.

When performing the method according to the present invention, the ureaconcentration values obtained by the urea monitor are used fordetermining the initial efficiency K/V of the dialyzer of the dialysistreatment. This requires that the urea monitor be connected for asufficient period of time so that a sufficient amount of data has beencollected. Usually, the efficiency is higher during the first 20 to 30minutes and then declines to a more constant value. Consequently, it isoften desired to wait for more than about 30 minutes before determiningthe initial or actual efficiency.

When the actual efficiency of a specific dialysis session has beenestablished, it can be assumed that the efficiency is approximatelyconstant if no other factors are altered. In reality, there is a smalldecrease in the efficiency over time, but it can be neglected for thepurposes of the present explanation. Of course, the computer for thedialysis machine can be programmed to take account of such knownvariations.

After determining that the limit value has been reached by any of theabove-mentioned methods, the computer 14 for the dialysis machine isprogrammed to change the efficiency, usually by decreasing it. Therelationship between the blood flow and the efficiency for a specificdialyzer can be included in the memory of the computer 14, and thecomputer can be programmed to change the efficiency as required, forexample stepwise or continuously according to an exponential curve.

The urea monitor is used for determining the new efficiency after eachalteration, and the efficiency values are integrated over time toindicate when a desired dose (Kt/V) of dialysis has been reached,whereupon the dialysis session may be ended. Of course, other methodsfor determining when the dialysis session should be ended may be used,such as manual or time controlled ending.

The same profiling method can also be used for hemodiafiltration andhemofiltration.

FIG. 5 shows an embodiment which is intended for hemodiafiltration. Allcomponents which are equal to the components of the hemodialysis machine1 shown in FIG. 4 have the same reference numerals as in FIG. 4.

In order to obtain the hemodiafiltration machine 15 of FIG. 5,essentially only a line 16 is added to the hemodialysis machine of FIG.4, connecting the outlet of flow meter 10 to the extracorporeal circuit5 for introducing a replacement fluid into the patient. The line 16 alsocomprises a pump 17 for controlling the amount of replacement fluidintroduced into the patient through the extracorporeal circuit 5. Ofcourse, the replacement fluid should be sterile.

The amount of ultrafiltration is still controlled by the pumps, 6 and 7,as measured by flow meters, 10 and 11. The volume of replacement fluidintroduced by pump 17 must be removed from the blood in the dialyzer,thereby increasing the filtration.

According to the present invention, the efficiency of the treatmentshould be varied, and usually decreased during the treatment. Such adecrease can be obtained by decreasing the blood flow in thehemodiafiltration machine 15 disclosed in FIG. 5. Another way ofdecreasing the efficiency would be to decrease the replacement fluidflow, until, ultimately, the treatment is converted to hemodialysis whenthe replacement fluid flow is zero.

Another embodiment of the present invention is disclosed in FIG. 6,which shows a hemofiltration machine 18. Some of the components are thesame as those in the embodiment of FIG. 4, and thus have the samereference numerals. However, the dialyzer 9 has no inlet line fordialysis fluid, but that line is replaced with a replacement fluid line19 comprising a pump 20, a flow meter 21 and a line 22 for connection tothe extracorporeal circuit 5 for introducing the replacement fluid intothe blood of the patient. FIG. 6 shows postdilution, where thereplacement fluid is introduced after the dialyzer, but also predilutionmay be used, where the replacement fluid is introduced into theextracorporeal circuit 5 before the dialyzer.

According to the present invention, the efficiency of the treatment isvaried or decreased by decreasing the replacement fluid flow and/or theblood flow. The ultrafiltration is maintained constant by the machine bymeans of the computer 14 calculating the difference between the flowmeters, 11 and 21, and controlling the pumps, 7 and 20, in dependence ofthe measured values.

Another embodiment of a hemofiltration machine 23 is shown in FIG. 7. Aportion of the inlet dialysis fluid is transferred to the outlet line 13through a short-circuit line 24. Another portion of the dialysis fluidis taken out through line 25 to form a replacement fluid metered bymeans of a pump 26. The portions are known to computer 14 via flowmeters, 10 and 11, and the speed of pump 26.

According to the present invention, the efficiency of the treatment isvaried or decreased by decreasing the speed of pump 26 and/or decreasingthe speed of pump 4.

As indicated above, other factors influence the dialysis treatment, andspecifically water removal or ultrafiltration. A high ultrafiltrationcan result in intradialytic symptoms, most commonly symptomatichypotension. However, it has been found that profiling of the efficiencywill also improve the patient's resistance against symptomatichypotension induced by high ultrafiltration during hemodialysis orhemofiltration.

Certain embodiments of the present invention have been described herein.It is clear to the skilled person that the present invention can bemodified and adapted to different dialysis machines and urea monitorswithin the scope of the invention. For example, other marker moleculesthan urea, such as creatinine, can be used for the purpose of thisinvention, whereby the urea monitor is replaced by a creatinine monitor.The invention can also be adapted to peritoneal dialysis.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

What is claimed is:
 1. A method of conducting a blood treatmentprocedure comprising conducting said blood treatment procedure at afirst predetermined efficiency and before reaching a first predeterminedtime limit value, said time limit value being determined on the basis ofa patient specific parameter, altering said first predeterminedefficiency to a second predetermined efficiency wherein said firstpredetermined efficiency is higher than said second predeterminedefficiency, and wherein said blood treatment procedure is selected fromthe group consisting of hemodialysis, hemofiltration andhemodiafiltration.
 2. The method of claim 1 wherein said secondpredetermined efficiency comprises a predetermined efficiency profileincluding at least a third predetermined efficiency.
 3. The method ofclaim 1 wherein said first predetermined time limit value is the timewhen a predetermined dialysis dose has been reached, said dialysis dosebeing a function of said first predetermined efficiency.
 4. A method ofconducting a blood treatment procedure comprising devising apredetermined profile of efficiency based on a patient specificcharacteristic curve for said blood treatment procedure, conducting saidblood treatment procedure at a first predetermined efficiency, andbefore reaching a first predetermined time limit value determined on thebasis of said characteristic curve altering said efficiency of saidblood treatment procedure in accordance with said predetermined profileof efficiency wherein said altered efficiency is lower than said firstpredetermined efficiency, and wherein said blood treatment procedure isselected from the group consisting of hemodialysis, hemofiltration andhemodiafiltration.
 5. The method of claim 4 including measuring anamount of urea removed by said dialysis and determining said firstpredetermined time limit value based upon removal of a predeterminedamount of said urea.
 6. The method of claim 5 including determining aurea generation rate for a specific patient and wherein saidpredetermined amount of said urea is based upon said urea generationrate.
 7. The method of claim 6 including determining said predeterminedamount of urea based upon the product of said urea generation rate, thetime between said dialysis procedure and a second dialysis procedure,and a predetermined patient factor.
 8. The method of claim 4 includingmeasuring the concentration of urea removed by said dialysis in thedialysis outlet fluid, and determining said first predetermined timelimit value based upon a predetermined concentration of said urea. 9.The method of claim 4 wherein said determining of said profile ofefficiency for said blood treatment procedure comprises altering atleast one of blood flow rate and a dialysis fluid flow rate through adialyzer.
 10. The method of claim 9 including devising a characteristiccurve of efficiency for a specific patient, wherein said determining ofsaid profile of said efficiency for said blood treatment procedure isbased upon a curve approaching said characteristic curve.
 11. The methodof claim 10 wherein said determining of said profile of said efficiencyis carried out stepwise or continuously.
 12. The method of claim 11wherein said predetermined profile of said efficiency is based upon theurea concentration of said dialysis fluid through said dialyzer, andwherein said determining of said profile of efficiency for said bloodtreatment procedure is based upon maintaining said urea concentrationupon said predetermined profile.
 13. Apparatus for conducting a bloodtreatment procedure comprising means for conducting said blood treatmentprocedure at a first predetermined efficiency, and means for alteringsaid first predetermined efficiency to a second, lower, predeterminedefficiency before reaching a first predetermined time limit valuewherein said predetermined time limit value is determined on the basisof a patient specific parameter, and wherein said blood treatmentprocedure is selected from the group consisting of hemodialysis,hemofiltration and hemodiafiltration.
 14. Apparatus for conducting ablood treatment procedure comprising means for devising a predeterminedprofile of efficiency based on a patient specific characteristic curvefor said blood treatment procedure, means for conducting said bloodtreatment procedure at a first predetermined efficiency, and means foraltering said efficiency of said blood treatment procedure in accordancewith said predetermined profile of efficiency, before reaching a firstpredetermined time limit value, wherein said first predetermined timelimit value is determined on the basis of a patient specific parameter,and wherein said blood treatment procedure is selected from the groupconsisting of hemodialysis, hemofiltration and hemodiafiltration. 15.The apparatus of claim 14 including means for measuring an amount ofurea removed by said dialysis, and means for determining said firstpredetermined time limit value based upon a predetermined amount of saidurea removed.
 16. The apparatus of claim 15 including means fordetermining a urea generation rate for a specific patient and means fordetermining said predetermined amount of urea removed based upon saidurea generation rate.
 17. The apparatus of claim 16 including means fordetermining said predetermined amount of said urea removed based uponthe product of said urea generation rate, the time between said dialysisand a second dialysis procedure, and a predetermined patient factor. 18.The apparatus of claim 14 including means for measuring theconcentration of urea removed by said dialysis, and means fordetermining said first predetermined limit value based upon apredetermined concentration of said urea.
 19. The apparatus of claim 14wherein said means for determining said profile of efficiency for saidblood treatment procedure comprises means for altering at least one ofblood flow rate and a dialysis fluid flow rate through a dialyzer. 20.The apparatus of claim 19 including means for devising a characteristiccurve of efficiency for a specific patient, wherein said means fordetermining of said profile of said efficiency for said treatmentprocedure is based upon a curve approaching said characteristic curve.21. The apparatus of claim 20 wherein said means for determining saidprofile of said efficiency is carried out stepwise or continuously. 22.The apparatus of claim 19 including means for determining apredetermined profile, and wherein said means for determining theprofile of said efficiency for said blood treatment procedure is basedupon a urea concentration of said dialysis fluid through said dialyzer.